1. Field of the Invention
The present invention relates to a method of manufacturing a vertical (vertical-electrode-type) gallium nitride-based light emitting diode (hereinafter, referred to as ‘vertical GaN-based LED’) which can enhance light extraction efficiency of a vertical GaN-based LED using a GaN substrate.
2. Description of the Related Art
Generally, a GaN-based semiconductor LED is grown on a sapphire substrate, but the sapphire substrate is a rigid nonconductor and has poor thermal conductivity. Therefore, there is a limitation in reducing the manufacturing costs by decreasing the size of a GaN-based semiconductor LED, or improving the optical output power and chip characteristic. Particularly, because the application of a high current is essential for achieving high power LED, it is important to solve a heat-sink problem of the LED. To solve this problem, there has been proposed a vertical GaN-based LED using a GaN substrate with excellent conductivity and transmittance.
Now, the problems of a conventional GaN-based LED will be described in detail with reference to FIG. 1.
FIG. 1 is a sectional view for explaining the conventional GaN-based LED.
As shown in FIG. 1, the vertical GaN-based LED includes an n-type GaN substrate 110, an active layer 120, and a p-type nitride semiconductor layer 130, which are sequentially formed on the n-GaN substrate 110, thereby forming a light-emission structure. The n-type GaN substrate 110 is formed to have a large thickness such that the active layer 120 and the p-type nitride semiconductor layer 130 are epitaxially grown thereon and are supported thereby.
On and under the light-emission structure, that is, on the p-type nitride semiconductor layer 130 and under the n-type GaN substrate 110, a positive electrode (p-electrode) 140 and a negative electrode (n-electrode) 150 are respectively formed.
More specifically, in the conventional vertical GaN-based LED, the GaN substrate with excellent conductivity and transmittance is used, instead of a sapphire substrate which is a rigid nonconductor and has poor thermal conductivity. Therefore, when nitride semiconductor layers such as the active layer 120 and the p-type nitride semiconductor layer 130 are formed on the GaN substrate, a lattice defect due to growth can be minimized by the same lattice shape. Further, it is possible to solve a heat-sink problem followed by high power.
However, in the conventional vertical GaN-based LED, the GaN substrate 110 is formed to have a considerably large thickness such that a plurality of nitride semiconductor layers having the same lattice are formed on the GaN substrate 110 through an epitaxial growth method.
In such a case, when the GaN substrate 110 has a large thickness, light emitted from the active layer is absorbed into or diffused throughout the GaN substrate, while passing through the GaN substrate with a large thickness. Therefore, light extraction efficiency decreases so that the overall luminance of the vertical GaN-based LED decreases.